The present invention relates generally to communication systems, and more particularly to a method and apparatus for re-establishing a call in a communication system.
Emergency service is widely provided as 9-1-1 service where a caller can reach emergency services such as police, fire, ambulance or the like by dialing 9-1-1. Enhanced 9-1-1 service provides the entity responsible for handling the emergency call, commonly referred to as the Public Safety Answering Point (PSAP), with the calling party""s location, directory number and other information related to the calling party. The PSAP is an emergency services network element that is responsible for answering emergency calls. Providing this information to the PSAP assists the PSAP in attempting to locate the calling party even if the calling party is unable to identify his or her location. This information also facilitates in re-establishing contact with the calling party if the original emergency call is terminated. Thus, the ability of a communication system to provide enhanced 9-1-1 service dramatically improves public safety.
In a typical landline 9-1-1 service application, an Automatic Number Identification (ANI) is associated with each customer landline phone such that there is a one to one relationship between ANI numbers and customer locations. When a calling party""s 9-1-1 emergency call is forwarded to the selective router switching system serving the 9-1-1 call, the call setup message includes the ANI number. An ANI data base, accessible by the selective router switching system, maintains a mapping of ANI numbers to emergency service areas. Specifically, the geographic area served by the switching system is divided into emergency service zones (ESZs) where each ESZ encompasses a portion of the customers hosted by the switching system. Thus, every ANI number is correlated with one of the ESZs, although each ESZ typically serves many ANI numbers. The switching system, after identifying the appropriate ESZ from the ANI data base, forwards the emergency call to the PSAP responsible for that ESZ. The ANI number is also forwarded to the PSAP in the call setup message.
While the above-described system works well for landline telephones, it is not possible to process emergency calls from mobile wireless devices in the same manner. Because mobile wireless communication devices are by definition not tied to a particular customer location, an ANI number for the mobile device cannot be translated to the present location of the device (the ANI number for a mobile device is typically correlated to the customer""s billing address).
Some mobile units are incapable of receiving incoming calls. This can happen when a mobile unit has roamed and does not have call delivery, when the mobile unit is a non-coded mobile unit, if the mobile service is discontinued, or if no roaming relationship exists between the service provider and the mobile unit""s home system. Using traditional 9-1-1 processing, the directory number of the mobile unit will be passed to the PSAP during the setup of the emergency call. If the emergency call is terminated and the PSAP desires to re-establish the emergency call, it will try to contact the mobile unit using the directory number of the mobile unit. Consequently, since the mobile unit is not able to be contacted via its directory number, the PSAP will fail in its attempt to re-establish the emergency call.
The problem of re-establishing a call is also true in a non-emergency setting. Therefore, a need exists for a method and apparatus for re-establishing a call, and more particularly an emergency call, where the directory number associated with the call is not effective in re-establishing the call.
It is an object of the present invention to provide a method and apparatus for enabling a called party to re-establish a call, and more particularly an emergency call, that has been terminated improperly.
The method and apparatus of the present invention enables a network element, such as a PSAP, to re-establish a call, such as an emergency call, with a mobile unit when the call has been improperly terminated. The present invention can also be effective in cases when a call has been properly terminated but more information is desired after termination of the call. When establishing the call, the MSC to which the mobile unit is connected determines if the mobile unit can be contacted using its directory number. If the mobile unit cannot be contacted with its directory number, the MSC associates the identification number of the mobile unit with a callback number. The MSC stores the identification number of the mobile unit with the callback number. The MSC establishes the call between the mobile unit and a network element, such as a PSAP, and includes the callback number in the setup of the call, similar to typical 9-1-1 processing.
If the call is improperly terminated, the present invention allows for the call to be re-established, preferably on the same call path, even if the mobile unit is one that cannot be reached using its directory number. The call may have terminated improperly due to the mobile unit temporally going into an area that does not provide cellular coverage, temporary loss of power, or any other situation where the link to the mobile unit is dropped, but the call was not desired to be ended by the called party. In typical emergency calls, the network element makes the decision to end the call, and it is upon communication of this decision to the MSC that the resources used for the emergency call are typically released.
If the call is improperly terminated, the network element will attempt to re-establish the call using the callback number passed during initial connection. Since the callback number is typically the directory number of the mobile unit, and because in this case the mobile unit cannot be reached by the directory number, this attempt to re-establish the call will be unsuccessful.
However, utilizing the present invention allows for calls to be re-established, preferably on the same call path, even in situations when the mobile unit that was a part of the original call has dropped out of the call and cannot be reached using its directory number. The MSC receives a request from the network element to re-establish the call. The MSC determines that the mobile unit cannot or should not be reached using the directory number of the mobile unit. This will preferably be done by comparing the callback number to a list of known callback numbers at the MSC that are used when the mobile unit cannot be contacted using its directory number.
The MSC then determines a way of contacting the mobile unit using means other than the directory number. The preferred method is to retrieve the Mobile Identification Number (MIN) for the mobile unit and then page the mobile unit using the MIN. Alternately, the International Mobile Station Identifier (IMSI) may be used. Once the MSC has contacted to mobile unit, the call can be re-established on the original call path.
Thus, the present invention provides an improved method and apparatus for re-establishing a call in a communication system.